Page 2 of 10

Introduction

For more than 30 years, MOS device technologies have been improving at a dramatic rate [1,2]. A large part of the success of the MOS transistor is due to the fact that it can be scaled to increasingly smaller dimensions, which results in higher performance. The ability to improve performance consistently while decreasing power consumption has made CMOS architecture the dominant technology for integrated circuits. The scaling of the CMOS transistor has been the primary factor driving improvements in microprocessor performance. Transistor delay times have decreased by more than 30% per technology generation resulting in a doubling of microprocessor performance every two years. In order to maintain this rapid rate of improvement, aggressive engineering of the source/drain and well regions is required. In this paper, key methods for improving device performance are discussed. Creating shallow source/drain extension (SDE) profiles for improved short channel effects, the use of retrograde and halo well profiles to improve leakage characteristics, and the effect of scaling the gate oxide thickness are discussed in detail. Fundamental tradeoffs and scaling trends in engineering these effects are analyzed through experimental data and computer simulations. The impact of these trends associated with circuit requirements including power supply, threshold voltage, and off-state leakage on transistor design is also explored. We show that the scaling trends of the last ten years will be extremely difficult if not impossible to maintain unless new methods for device improvement are found. In addition to the conventional MOS transistor, several alternate device architectures are analyzed to understand the potential gains and tradeoffs associated with each device. The ability to overcome current physical technology limits such as gate oxide thickness and shallow junction formation as well as tradeoffs in circuit design will determine if MOS transistors can be scaled into the next century.

    Page 2 of 10